This invention relates to nuclear reactors and to collecting trays for molten nuclear fuel debris.
In one form of nuclear reactor a nuclear fuel mass constituting a reactor core is submerged within a pool of liquid coolant which serves as a vehicle for the transfer of heat from the reactor core to steam generating equipment. Examples of reactors of this form are the liquid metal cooled fast breeder reactor, boiling and pressurised water reactors. In the event of loss of coolant from the core, or restricted flow of coolant through the core, the nuclear fuel could melt down and fall to the floor of the coolant containing vessel. Because of the high heat content of the fuel debris supplemented by fission produce decay heat and, possibly, by criticality of the nuclear mass, serious damage could be caused to the floor of the vessel and its environment. For a liquid metal cooled fast breeder reactor several proposals have been made for retaining molten fuel debris before it reaches the floor of the vessel one such proposal including the provision of a plurality of layers of collecting trays disposed beneath the core, trays in the upper layers being arranged to overlap trays in the lower layers. However, the trays would be subject to such high heat flux that serious distortion could occur.